Therapeutic intermittent positive pressure respirator



Mgr-ch 1969 M. o. LISTON 3,434,471

THERAPEUTIC INTERMITTENT POSITIVE PRESSURE RESPIRATOR Filed April 6,1966 INVENTOR. MAX .0. L/srou BY H/S ATTORA/ETS HARE/5; K/EcH, RUSSELL &KER/v US. Cl. 128-1458 Claims ABSTRACT OF THE DISCLOSURE An intermittentpositive pressure respirator including an automatic control forproviding constant volume pulses of air or other breathable fluid to auser at predetermined intervals and providing an override responsive tothe users demands to provide a shorter interval. The automatic controlincludes a control chamber having a diaphragm which is coupled to themain supply valve to close off the passage of breathable fluid to theuser, said diaphragm moving in response to a controlled pressure changewithin said chamber. A humidifier, heat exchanger and temperaturecontrol means are included for delivering air to the user atsubstantially 100 percent relative humidity and body temperature.

This invention relates to a breathing apparatus and more particularly toa respirator which supplies pulses of air substantially independently ofthe patient, thereby forcing him to breathe, but which is automaticallyresponsive to a patients requiring additional air to reduce the intervalbetween pulses and thereby supply such additional air.

Many persons who suffer from respiratory defects or illnesses requireassistance in breathing. Respirators gen erally supply air, oxygen, andmedicated fluids to a face mask worn by the patient or the air, oxygen,and medicated fluids may be fed directly into the trachea. In manyinstances it is desirable that the respirator supply a fixed quantity ofair in each pulse or breath substantially independently of theresistance of the respiratory system or the lung compliance. With thisconstant volume type of machine, the patient is in effect forced tobreathe.

One difficulty with a typical constant volume machine is that thepatient may suddenly demand additional air. In other instances, it maygenerally be difficult for the patient to synchronize his breathingefforts with the output of the respirator. Thus, it would be desirableto have a respirator which would normally deliver a constant volume ofair in each breath and at constant intervals, but which is alsoresponsive to peculiar demands of the patient for additional air toreduce the interval between the constant volume pulses of air. Prior artmachines are not this flexible.

Another difficulty with some prior art machines is that they have failedto provide an alternate supply of air in case of failure or airstoppage. In addition, many of the prior art respirators supply airwhich is much too dry for use by certain patients.

Accordingly, a primary object of this invention is to provide arespirator which normally provides constant volume pulses of air atconstant intervals, but which will automatically vary the intervalbetween breaths in response to unusual breathing requirements of thepatient.

A further object of this invention is to provide a constant volumerespirator which is adjustable to vary the volume and the timing, andone which utilizes a pneumatic timing control system.

A further object of this invention is to provide a humidifier for arespirator that will deliver air at substantially atent O relativehumidity at body temperature to the patient.

The objects of this invention may be accomplished by providing passagemeans connectible to a source of breathable fluid for conducting thelatter to the patient and valve means for controlling the flow of thefluid through the passage means. A valve operator controls the openingand closing of the valve substantially independently of the patientthereby establishing an automatic program for the valve. Override meansresponsive to the patients beginning inspiration prior to the timeestablished therefor by the automatic program opens the valve therebyreducing the normal interval between breaths. An exhaust passage throughwhich the patient may exhale may also be provided. A relief valve blocksthis expiration passage during inspiration and permits its openingduring expiration.

It is also desirable to provide a humidifier that will supply air to thepatient at substantially 100% relative humidity at body temperature. Thehumidifier is particularly useful when a tracheotomy is being performedbe cause in its absence the relatively dry air, which is supplieddirectly to the trachea, would dry the latter thereby irritating thetrachea membranes. The humidifier is constructed so that it can bepositioned close to the patient to prevent substantial change ofcondition of the air supplied thereby. The system provides forcontrolled overheating of the air, addition of water vapor, cooling andcondensing, and delivery to the patient at the desired temperature andhumidity.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof may thus beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which:

FIG. 1 is a semidiagrammatic View of a respirator with the automaticvalve therefor being shown in longitudinal section;

FIG. 2 illustrates a humidifier and several safety devices adapted foruse with the respirator of FIG. 1; and

FIGURE 3 is a circuit diagram of a temperature control circuit for thehumidifier of FIGURE 2.

:Referring to the drawing, a fluid which may be made up of air, oxygen,and a medicinal agent is supplied to a bistable regulator 11 by supplylines 13, 15, and 17, respectively, and an inlet manifold 19. Thesefluids pass through flow meters 21, check valves 23, and flow controlvalves 25 to the supply manifold 19.

The fluid passes through a passage 27 within the regulator 11, a conduit29, a reservoir 31, a flow control valve 33 in the conduit 29, ahumidifier 35 (FIG. 2), and a conduit 37 to an outlet 39 which may bedirectly connected into the respiratory system of the patient.

The fluid can only flow through the path outlined above as permitted bythe regulator 11. The regulator 11 includes a housing 41 connected tothe supply manifold 19 and the conduit 29 as illustrated. A normallyopen supply valve 43 mounted in the housing 41 controls the flow offluid through the passage 27 to the patient. The valve 43 is maintainedin the normally open position by a spring (not shown) or a bellows 45which is sealed to the housing 41 and which communicates with thepassage 27 through a plurality of inlet ports 47. The bellows 45 extendsinto a recess 49 in the housing 41, which is vented to the atmospherethrough an aperture 51.

A diaphragm 53 and a wall 55 of the housing 41 form an operating ortiming chamber 57 which receives fluid from the supply lines 13, 15, and17 through the conduit 29, a lateral passage 59, a needle valve 61, aCheck valve 63, and an inlet port 65. The rate of fluid flow into theoperating chamber 57 is controlled by the needle valve 61. When thepressure within the operating charnher 57 reaches a predetermined value,which is a pressure suflicient to overcome the opposing pressure in thebellows 45 plus the small bellows spring force, the diaphragm 53 isforced outwardly to rapidly and tightly close the normally open valve43.Thus, the diaphragm 53 acts as a valve closure means for closing thenormally open valve in response to a predetermined increase in pressurein the operating chamber 57. Once the valve 43 is closed, the pressurein the bellows 45 reduces to atmospheric. Then the pressure in theoperating chamber 57 must drop almost to atmospheric before the valve 43can reopen. Thus the valve 43 functions in the nature of a bistable oron-ofi device.

During normal operation of the respirator, the fluid will exhaust fromthe operating chamber 57 through an exhaust port 67, a conduit 69, acheck valve 71, and a needle valve 73. The needle valve 73 can beadjusted so that any desired predetermined amount of time will berequired for the fluid to drain out of the operating chamber. During thetime when the valve 43 is open and fluid is flowing through the conduit29, none of the fluid will drain from the operating chamber 57 throughthe conduit 69 because the pressure in the conduit 29 will be at leastas great as that in the operating chamber. However, when the valve 43closes and the patient has drawn much of the fluid from the conduit 29into his respiratory system, a pressure differential exists whichpermits exhausting of the operating chamber 57 through the conduit 69.

It is apparent that the exhausting of the operating chamber 57 willreduce the pressure on the diaphragm 53 and allow the normally openvalve 43 to open. During normal operation of the respirator, the valve43 will open and close at fixed intervals to supply equal volumes of airin the pulses or breaths. Likewise, the intervals between breaths willbe constant. Thus, the valves 61 and 73 provide an automatic program forthe valve 43.

The amount of air supplied by the respirator in each pulse can beadjusted by adjusting the needle valve 61. Thus, if the needle valve 61is open a large amount, the operating chamber 57 fills more rapidly tocause the valve 43 to close more rapidly. This results in a lesserquantity of air being supplied by the respirator in each pulse.Conversely, partially closing the needle valve 61 results in a largeramount of air being supplied in each pulse.

The interval between pulses of air can be similarly varied. Thus, thelarger the opening provided by the needle valve 73, the sooner thepressure in the operating chamber 57 will decrease to the point at whichthe normally open valve 43 can return to its normally open position.Conversely, the greater the impedance to flow through the conduit 69provided by the needle valve 73, the greater the interval between pulsesof air.

Sometimes a patient will be unable to synchronize his breathing with theoutput from the respirator. This will occur, for example, when thepatient feels a need for an increased amount of air. Accordingly, one ofthe features of this invention is to provide override means which areresponsive to the patients beginning inspiration prior to thetermination of the interval between breaths which has been establishedby the needle valve 73 for prematurely opening the valve 43. Thisoverride function is accomplished by rapidly venting the operatingchamber 57 in response to the patients attempts to inspirate prior tothe time the operating chamber pressure has been reduced sufficiently toallow the valve 43 to open. The wall 55 and a second diaphragm 75 definean exhaust manifold 77, and the housing 41 and the diaphragm 75 form ademand cavity 79. Air can be exhausted from the operating chamber 57through an outlet 81 formed in the wall 55, the exhaust manifold 77, andan exhaust port 83 in the outer wall of the housing 41 to theatmosphere. A valve 85, which is seated in the outlet 81 controls theexhausting of air frgm the operating chamber 57.

A spring 87 normally biases the valve 85 to the closed position. Thepressure in the demand cavity 79 and the spring 87 control the movementsof the valve 85 and hence the exhausting of air from the operatingchamber 57 through the outlet 81. A conduit 89 interconnects the demandcavity 79 and the conduit 29 downstream of the valve 43 thereby causingthe pressure in the demand cavity to be substantially the same as thepressure in the conduit 29 downstream of the valve 43. A pressure gage90 may be installed on the conduit 89.

The operation of the portion of the respirator illustrated in FIG. 1 isas follows. Fluid is supplied through the supply manifold 19, theregulator 11, the reservoir 31 and the conduit 29 to the patient. Theend of the conduit 29 shown in FIG. 1 may be connected to a face mask orother devices for transmitting the fluid into the nose or mouth of thepatient. The purpose of the reservoir 31 is to reduce the rate of changeof fluid flow from the respirator to the patient. Initially, fluid willflow through the normally open valve 43 and the inlet ports 47 to thebellows 45 to expand the latter and open the valve 43 a greater amount.Fluid will also flow through the lateral passage 59 as permitted by theneedle valve 61 into the operating chamber 57. When the pressure in theoperating chamber 57 is sufficient to overcome the force tending to holdthe valve 43 in the open position, the diaphragm 53 will rapidly forcethe valve 43 to a closed position. During the time the valve 43 is open,the user is receiving air and, accordingly, the closure of this valvemarks the end of inspiration. When the valve 43 closes, the patient willutilize enough of the air in the conduit 29 to reduce the pressuretherein to about atmospheric. This pressure reduction in the conduit 29allows the fluid in the operating chamber 57 to flow through the conduit69 into the conduit 29, and when the pressure in the operating chamberis sufl'iciently low, the normally open valve 43 will return to itsnormally open position and the cycle will be repeated.

During the time the valve 43 is closed, the patient Will be exhaling. Ifthe patient begins inspiration prior to the time that the valve 43 hasreturned to its normally open position, the pressure in the conduit 29will drop below atmospheric. The pressure in the demand cavity 79 willdrop accordingly, and the diaphragm 75 will cause the valve 85 to openthe outlet 81 to exhaust the operating chamber through the exhaustmanifold 77 and the exhaust port 83. This causes the valve 43 to openimmediately and supply air to the patient. In actual practice it hasbeen determined that the valve 85 will operate reliably in response to anegative pressure of only one centimeter of water. Thus, the regulator11 responds immediately to the demands of the patient for an additionalbreath of air. As soon as the valve 43 opens, the pressure in theconduits 29 and 89 and hence the demand cavity 79 rapidly becomessufficient to close the valve 85.

Referring to FIG. 2-, the fluid passes from the conduit 29 into thehumidifier 35. The humidifier is usually used when a tracheotomy isbeing performed, in which case the outlet 39 may deliver air directlyinto the trachea. Bypassing of the nose and mouth results in a drying ofthe trachea with resulting crustations and other irritations to thetrachea membranes. Bacterial growths and heavy secretions in therespiratory system frequently result. These undesirable conditions existeven where the incoming air is delivered at relative humidity at roomtemperature. It has been found that the incoming air should be at 100%relative humidity at body temperature, which calls for considerablyhigher water content of the air. At the same time, the temperature ofthe air must be closely controlled as the delivery of air at 100%relative humidity at a temperature in excess of body temperature wouldresult in condensation within the respiratory system of the user. Thehumidifier and associated elements of FIG. 2 provides this desiredoperation in a respirator. The humidifier is quite small and may bepositioned close to the patient thereby reducing the dead space in theconduits and eliminating excessive cooling of the gases, resulting in aclosely controlled air supply system.

The humidifier 35 includes a container 91 for holding a quantity ofwater 93. A first heat exchanger 95 is mounted in the container 93 andextends vertically thereabove to a location at which it is connected tothe conduit 29. Typically the heat exchanger 95 is a block of metal andincludes an elongated shell 97 having an aperture 99 formed therein justabove the water level within the container 91 and an electrical heater101 preferably disposed below the water level in the container 91 andsupplied with electrical power through a connector 103. The heater 101heats the incoming fluid from the conduit 29 and also heats the water93. The container 91 is closed by a cover 105 and the heated water formsa vapor in a head space 106 of the container 91 between the top of thewater 93 and the cover.

The breathable fluid from the conduit 29 passes through the heatexchanger 97 Where it is heated to a temperature above body temperature,typically 5060 C., and passes out through the aperture 99 and into thehead space 106 where it becomes saturated with water vapor. Themoisture-laden flui'd will then pass out of the container 91 throughanother heat exchanger 107, the conduit 37, and the outlet 39 to therespiratory system of the patient. The air is cooled somewhat in passingthrough the heat exchanger 107 and some of the moisture thereincondenses, assuring 100% relative humidity at the exit temperature. Bothheat exchangers 97 and 107 may incorporate a metal sponge or similarmaterial in the air flow passages for improving the heat transfercharacteristics.

The temperature of the air at the inlet to the patient is controlled bysensing the air temperature and varying the output of the heater 101.This form of temperature control is highly desirable, since the volumeof air intake varies over wide ranges and fixed temperature systems donot provide satisfactory results. In the embodiment illustrated, atemperature sensing element, such as a thermistor 109, is positioned atthe outlet 39, as close as practical to the inlet to the patient. Thethermistor 109 is connected into a control circuit, as shown in FIG. 3,for varying the power supply to the heater 101. The heater 101 isenergized from an A.C. source through a silicon controlled rectifier102. The thermistor 109 is connected in series with a resistor 110across a D.C. source so that variations in resistance of the thermistorwill produce corresponding variations in the control voltage applied tothe silicon controlled rectifier 102. The resistor 110 preferably is avariable resistor to permit initial adjustment of the system. An A.C.modulation may be coupled into the resistor circuit via a transformer112, if desired. Under steady state conditions, the resistor 110 isadjusted to deliver air to the patent at the desired body temperature.This means that air leaving the humidifier will be saturated at a highertemperature, will be cooled in the second heat exchanger with theabsolute humidity being reduced and will be delivered at the patientsinlet at the desired temperature and humidity. If the rate of air intakeincreases, the control system will provide for additional heat from theheater to maintain the desired temperature. Similarly, if the rate ofair intake decreases, the control circuit will reduce the heat input tomaintain the desired temperature.

A relief valve is provided adjacent the heat exchanger 107 and includesan annular valve seat 113 having a pressure-responsive valve member orcounterweight 115 slidably mounted thereon. The pressure within thesystem acts on the lower side of the valve member 115 through openings111 and, if such pressure becomes excessive, the valve member orcounterweight 115 will be forced upwardly off the seat 113 to exhaustthe system to atmosphere. This counterweight type of relief valve ispreferred because of its simplicity.

An expiration passage is provided through which the patient may exhale.In the specific embodiment illustrated, the conduit 37 and a relief orexhaust valve 117 form the expiration passage. The valve 117 is normallyclosed and is connected to the conduit 37 through the heat exchanger107, which also functions as a manifold. The valve 117 includes a valvehousing 119 defining an outlet 121, a movable valve member 123, and avalve seat 125. A

spring 127 normally urges the valve member 123 toward.

the valve seat 125.

Means are provided to close the valve 117 when the valve 43 is opened sothat the valve 117 will be locked in the closed position duringinspiration. Such means includes a bellows 129 mounted in the valvehousing 119 and defining therewith a valve operating chamber 131. Aconduit 13-3 connects the conduit 29 to the operating chamber 131 sothat the pressure in the operating chamber 131 will be substantially thesame as the pressure in the conduit 29 downstream of the reservoir 31.

When the valve 43 is open, fluid under pressure is supplied through theconduit 133 to the operating chamber 131. This fluid under pressureextends the bellows 129 to cause the valve member 123 to seat and closethe valve 117. Thus, the valve 117 is always closed during inspiration.When the valve 43- closes, the pressure in the conduits 29 and 133decreases and the bellows retracts, with the spring 127 holding thevalve closed.

The respirator described herein provides constant volumes of air to apatient at fixed predetermined intervals substantially independently ofthe lung compliance of the patient. The patient is therefore forced tobreathe at the machine rate. However, the amount of air supplied by themachine in each pulse and the interval between pulses are variable overa wide range by making the appropriate adjustments of the needle valves61 and 73. If the patient should unexpectedly require additional air,the respirator will supply it automatically in response to his effortsto obtain breaths more rapidly. The humidifier and associated equipmentwill produce air at substantially relative humidity at body temperature.The counterweight type relief valve 107 guards against overpressures inthe system.

Many changes, modifications, and substitutions may be made by one havingordinary skill in the art without necessarily departing from the spiritand scope of this invention.

What is claimed is:

1. In a respirator for supplying a breathable fluid to a user, thecombination of:

a source for providing the breathable fluid under pressure;

inlet means for delivering the breathable fluid to the user;

a humidifier for supplying water vapor to the breathable fluid andincluding a heater for heating the incoming breathable fluid to atemperature above body temperature;

a heat exchanger for cooling the breathable fluid passing therethrough;

valve means between said source and said inlet means to control the flowof fluid from said source to said inlet means;

conduit means coup-ling said source, valve means, hu-

midifier, heat exchanger and inlet means for flow of the breathablefluid from the source the valve means, humidifier, heat exchanger andinlet means to the user;

temperature sensing means positioned at said inlet means for sensing thetemperature of the breathable fluid adjacent the point of delivery tothe user; and

control means having said temperature sensing means as an input forcontrolling said heater to vary the temperature of the breathable fluidleaving said humidifier to maintain the temperature of the breathablefluid at said inlet means substantially at body temperature.

7 8 2. In a respirator for supplying a breathable fluid from saidoperating chamber, said normally open valve a source to the inlet meansof a user, the combination of: means returning to its normally openposition in repassage means for connecting the source of thebreathsponse to a predetermined decrease in pressure in able fluid tothe inlet means of the user; said operating chamber; and valve means forcontrolling the flow of the fluid override means responsive to the usersbeginning inthrough said passage means; spiration prior to thetermination of said interval valve operator means for automaticallyopening and between pulses for overriding said automatic proclosing saidvalve means substantially independently gram and opening said valvemeans for shortening of the user at predetermined intervals therebycausthe interval between pulses, said override means ining constantvolume pulses of the breathable fluid to 10 eluding means forprematurely causing said predeterbe supplied to the user atpredetermined intervals, mined decrease in pressure in said operatingchamber said valve operator means thereby establishing an therebycausing opening of said valve means prior to automatic program for saidvalve means; the time established therefor by said automatic prooverridemeans responsive to the users beginning ingram comprising spirationprior to the termination of said interval a demand h b between pulsesfor overriding said automatic promeans connecting id d d h b to aid gfamand Opening Said Valve means for Shortening the sage means downstream ofsaid valve means, the interval bfitwecn P 3 pressure in said demandchamber being reduced at a humidifier for P Y Water Vapor to the breatheleast to a third predetermined amount when the user ble fluid andincluding a heater for heating the incoming breathable fluid to atemperature above body temperature;

a heat exchanger for cooling the breathable fluid passing therethrough,said humidifier and heat exchanger being connected in said passage meansbetween said valve means and the user;

begins inspiration, and means responsive to the reduction of thepressure in said demand chamber to said third predetermined amount forrapidly venting said operating chamber to allow said normally open valvemeans to open. 4. A combination as defined in claim 3 includingextemperature sensing means positioned in Said passage haust valve meansin said passage means for venting said means adjacent the user forsensing the temperature Passage means to the atmosphere duringeXPITatIOH and of the breathable fluid adjacent the point of deliveryincluding 11 first PI'BSSHre responsive Valve Operating means to theuser; and responsive to the pressure in said passage means downcontrolmeans having said temperature sensing means stream of said normally openvalve means for closing said as an input for controlling said heater tovary the exhaust valve means during inspiration and a second temperatureof the breathable fluid leaving Said pressure responsive valve operatingmeans responsive to midifier to maintain the temperature of the fluid inh Pressure i id passage means for opening said the Passage meansadjacent the user substantlany at haust valve means during expiration,with said first operbody temperature. ating means overriding said secondoperatin means dur- 3. In a respirator for supplying a breathable fluidfrom a source to the inlet means of a user, the combination of:

passage means for connecting the source of the breathable fluid to theinlet means of the user;

normally open valve means disposed in said passage means for controllingthe flow of the fluid through said passage means and valve means; Passmgtherethl'oughi valve Operator means for automatically Opening andcontrol means ad acent the inlet means for controlling closing saidvalve means substantially independently the lemperatum 0f flllld v r d tthe user. of the user at predetermined intervals thereby causingconstant volume pulses of the breathable fluid ing inspiration.

5. A combination as defined in claim 4 including: a' humidifier in saidpassage means downstream of said normally open valve means; a heatexchanger in said humidifier for heating the fluid References Cited tobe supplied to the user at predetermined intervals, UNITED STATESPATENTS said valve operator means thereby establishing an 1,950 5773/1934 Stephenson automatic program r Said valve means, Said valve 602,1211311 6/1938 Anderson J51. 128145.8 p r means mcludms 2,547,4584/1951 Goodner 128145.8 n operatmg chamber, 3,068,856 12/1962 Bird etal. 128145.5 means for conducting the breathable fluid at a first pre- 3075 523 1/1963 Eichelman X determined rate from a location in saidpassage 3O97638 7 /1963 Streimer X means downstream of said normallyopen valve 3171411 3/1965 Levine X means to said operating chamber toincrease the 3:267:935 8/1966 128 145 5 P therem: 3,307,542 3/ 1967Andreasen 128-145 8 means for returning the fluid at a secondpredetermined rate from said operating chamber to said passage RICHARDGAUDET Primary Examiner. means downstream of said normally open valvemeans to decrease the pressure in said operating KYLE L-HowELLA-gslsmmExamine"- chamber, and means for closing said normally open valve meansin response to a predetermined increase in pressure in 128192

